Amyloglucosidase (AG) finds broad commercial use in the conversion of partially hydrolyzed starch, or thinned starch, to glucose. Processes for glucose production most often use soluble AG in a batch mode. Although the use of an immobilized AG (IMAG) has many desirable features, the maximum glucose levels (G.sub.max) attainable using an IMAG are lower than those routinely available in processes using soluble AG. This limitation in G.sub.max is a severe handicap which has sharply curtailed the commercial development of IMAG. For example, many commercial processes are geared to a glucose level of at least 94.0% in the starch saccharification product, and product with glucose levels of even several tenths of a percent under that is unsuitable.
The lower G.sub.max attained when using IMAG appears to result from pore diffusion effects. In particular, it is believed that glucose which is formed in the smaller pores of an IMAG tends to have a longer residence time in an AG environment because of slow diffusion than does glucose which is formed in the larger pores of the support matrix. Since AG also catalyzes the irreverisble formation of a reversion product, isomaltose, the retention of glucose in the smaller pores leads to increased reversion product and a decreased G.sub.max. The bitterness of isomaltose further exacerbates the effects of slow pore diffusion since glucose syrup often is used for its sweetness properties.
The invention herein is based on the surprising discovery that maximum glucose levels attained with aged IMAG are about 1% higher than those attained with fresh IMAG. The origin of this phenomenon is not known with certainty, but it is believed to arise from the lower reaction rate in aged IMAG, which lessens the effect of pore diffusion resistance, thereby allowing a higher G.sub.max. That is, that glucose may have a longer residence time in an AG environment because of slow diffusion becomes less important as the reaction rate with the AG decreases. However uncertain may be the cause of a higher G.sub.max, the fact of a higher G.sub.max from aged IMAG is beyond cavil.